The role of the intercellular matrix in dermal calcinosis of the CRST syndrome. An electron-microscopic study.

We performed an electron-microscopic study on calcium deposits in two patients with calcifying scleroderma (CRST syndrome). Calcium deposits were detected both intracellularly in the mitochondria of phagocytic cells and extracellularly. Needle-like crystals measuring up to 4,500 angstrom in length and approximately 60 angstrom in width were present in both the Von Kossa-positive regions and the apparently normal dermal areas around the calcification sites. Although the fibrillar matrix's ultrastructure was normal, hollow oxytalan fibrils were detected. Slightly electron-opaque, star-shaped material was observed among the fibrillar component of the matrix (matrix granules), which is the ultrastructural expression of some types of proteoglycans containing keratan sulphate and condroitin sulphate. These granules cannot be detected in normal dermis. The extrafibrillary calcium deposits on these mucopolysaccharide structures may represent an early event in the complex pathogenesis of calcification in the CRST syndrome.